In the power transmission apparatus of vehicle, and the like, driving force is transmitted to driving wheels from a transmission by way of a drive shaft that comprises a shaft and a constant-velocity universal joint. As illustrated in FIG. 10, the drive shaft has a shaft 83, and joints 41, 42 that are placed at the axial opposite ends of the shaft 83. One of them, the joint 41, is connected with a driving member, such as a differential device, on the inboard side; and the other one of them, the joint 42, is connected with a driven member, such as a driving wheel, on the outboard side.
The joints 41, 42 are a ball type, for instance. The joints 41, 42 comprise an inner race 8 in which a plurality of ball grooves 81 are formed at equal intervals in the peripheral direction, balls 80 which roll within the ball grooves 81, and an outer race 7 which accommodates the ball grooves 81 of the inner race 8 and the balls 80 in the cupped portion 70. The inboard-side joint 41 transmits rotary torque at constant velocity from the input-side outer race 7 to the output-side inner race 8 by way of the rollable balls 80. The outboard-side constant-velocity universal joint 42 transmits rotary torque at constant velocity from the input-side inner race 8 to the output-side outer race 7 by way of the rollable balls 80. Both of the constant-velocity universal joints 41, 42 are covered by means of a bellows-structured boot 1 in which grease is sealed so that the intrusion of foreign materials is prevented, and thereby their smooth rotations at large angles are maintained.
This boot 1 for constant-velocity universal joint has a major-diameter cylindrical portion 2 being retained to the outer race 7, a minor-diameter cylindrical portion 3 having a smaller diameter than that of the major-diameter cylindrical portion 2 and being retained to the shaft 83, and a substantially-truncated-cone-configured stretchable bellows portion 19 connecting the major-diameter cylindrical portion 2 with the minor-diameter cylindrical portion 3 integrally. At the time of service, the bellows portion 19 deforms in compliance with angles (joint angles) that the outer race 7 and the shaft 83 make. Accordingly, the boots 1 seal the joints 41, 42 securely by means of the deformation of the bellows portion 19, even when the joint angle becomes larger.
In order to assemble a drive shaft, first of all, the balls 80 are put in place in the ball groves 81 of the inner races 8 that are fixed to the both axial opposite ends of the shaft 83. Next, the inner races 8 are fitted into the inside of the cupped portion 70 of the outer races 7. Then, the minor-diameter cylindrical portion 3 of the boots 1 is fixed to the shaft 83 with a clamp 30. Moreover, the major-diameter cylindrical portion 2 of the boots 1 is fixed to the cupped portion 70 of the outer races 7 with a clamp 20.
Upon assembling the drive shaft with a vehicle, the shaft 83 is gripped at around the middle with a hand 85, and is then raised, as illustrated in FIG. 15. Around the inner races 8 that are fixed at both axial opposite ends of the shaft 83, the outer races 7 are placed by way of the rotatable balls 80. Accordingly, when the shaft 83 as raised, the outer races 7 with predetermined weight hang downward from both opposite ends of the shaft 83. On this occasion, the bellows portion 19 of the boots 1 deforms diametrically, and thereby the boots 1 might have interfered with the balls 80 inside the cupped portion 70 of the outer races 7. Sometimes, the boots 1 might not be provided with rigidity to such an extent that they can limit the movements of the balls 80, and thereby the balls 80 might have come off from the outer races 7, as shown in FIG. 16. In order to assemble the balls 80 inside the outer races 7, the boots 1 are removed from the joints 41, 42. Next, the joints 41, 42 are disassembled. Thereafter, the inner races 8 are assembled again with the balls 80 and outer races 7 to constitute the joints 41, 42, thereby fixing the boots 1 onto the joints 41, 42. Thus, when the balls 80 come off from the outer races 7, it is needed to carry out the disassembly/assembly of the joints 41, 42 again, and it is troublesome. It is believed that the balls 80 come off from the outer races 7 because the part of the bellows portion 19 of the boots 1, part which is close to the major-diameter cylindrical portion 2, has a bellows configuration so that the rigidity is weak and accordingly it is likely to deform.
Moreover, as an example of ball-type constant-velocity universal joint, cross-grooved constant-velocity universal joints are available. In cross-grooved constant-velocity universal joint, the ball locus in the outer-race ball grooves and the ball locus in the inner-race ball grooves cross one another peripherally. In such a cross-grooved constant-velocity universal joint, it as needed to prevent the balls, which constitute the constant-velocity universal joint, from coming off from the outer races in the course of assembly, in the course of conveyance after assembly and before being installed to a vehicle and the like, and so forth.
As one of the measures for this, for example, in FIG. 2 of Japanese Unexamined Utility Model Publication (KOKAI) Gazette No. 1-69, 916, the following are set forth: a metallic fitting is put in place on the opening side of the outer races, thereby limiting the joint angle by means of bringing the shaft into contact with the aforesaid metallic fitting; as a consequence it is adapted so that the balls do not come off from the outer races. Moreover, in FIG. 1 of aforesaid Japanese Unexamined Utility Model Publication (KOKAI) Gazette No. 1-69, 916, instead of the aforementioned metallic fitting, using boots that have rigidity being equal to that of the aforesaid metallic fitting is set forth. In addition to these, in Japanese Unexamined Utility Model Publication (KOKAI) Gazette No. 6-32, 755, the following are set forth: a circlip is put in place on the inner peripheral surface of the opening end of the outer races, thereby limiting the joint angle by means of bringing the balls into contact with the circlip; as a consequence it is adapted so that the balls do not come off from the outer races.